Valortim is the name of the experimental drug that volunteers will receive in this study. Valortim may also be called MDX-1303. Experimental means that the drug is not yet approved by the Food and Drug Administration (FDA). Valortim is a monoclonal antibody (laboratory-made immune system molecule) for the treatment of inhalation anthrax (when the infection starts in the lungs). Valortim works by attaching itself to part of the anthrax toxin preventing the toxin from doing damage to cells. This study is being conducted to see if Valortim given over 120 minutes is safe and tolerable. This study will take place in five parts: Screening Phase, Check-in Phase (the day you arrive at Quintiles to start the study), Treatment Phase (the time when you receive the study medication), Follow-up Phase (the time after you receive the study medication) and Final Visit.

Twenty-eight subjects will be recruited and entered into one of three dose groups 1mg/kg, 5mg/kg, 10mg/kg or placebo. Subjects will be stagger dosed into one of the three groups and randomly assigned to receive Valortim or saline. Subjects will reside in the clinical trial Phase I Unit from Day -1 through Day 2. After discharge on Day 2, all subjects will return to the Phase I unit 7 times at specified time points over an additional 130 days post-dosing (133 days total participation from check-in on Day -1)or placebo.

Inclusion Criteria:

1.Subject must have read, understood, and provided written informed consent 2.Subjects should be in generally good health, based upon pre-study medical history, physical examination, laboratory testing and ECG 3.Laboratory screening values (i.e., hematology, clinical chemistries and urinalysis tests) must be within study-defined ranges 4.No detectable antibody to B. anthracis Protective Antigen (PA-IgG) as measured by ELISA testing at study Screening 5.Women of childbearing potential and sexually active males may be enrolled if protocol specific contraceptives or practices are met 6.Agreement to not receive any vaccinations Day -1 through to 29 days post dosing. Vaccination against B. anthracis is prohibited during the study.8.Body Mass Index (BMI) ≥ 19 and ≤ 30. 9. Abstinence from alcohol for 24 hours prior to study drug

Exclusion Criteria:

1. Prior known or suspected exposure to B. anthracis 2. Prior vaccination for B. anthracis 3.Prior exposure to Valortim as part of a previous clinical trial 4.Immunoglobulin E (IgE) level at screening that is above the upper limit of normal per the laboratory's reference range 5. History of drug or alcohol abuse, i.e., having been treated either in an in-patient or out-patient facility within 12 months of study Screening 6. Outward signs of active allergies or upper respiratory infection 7. History of dizziness or fainting upon standing (orthostatic hypotension) which, in the opinion of the Investigator, may interfere with safety evaluations 8. Positive drug result and/or positive alcohol result at time of study Screening or at Day -1